Overdrive or not
- Thread starter Jester
- Start date
Lee Stockwell
FOJL
Depends on terrain and traffic.
G
Guest
Guest
On my chevy van overdrive is always engaged. Seems to run better.
Dolly Llama
Number 5
I never do unless I'm pulling a trailer.
..L.T.A.
..L.T.A.
The Great Oz
Member
The regular Chevy and Ford OD transmissions will hunt between third and fourth when driving a steady thirty five to forty miles per hour. This can cause the transmission to suffer damage from overheating, so the GM dealer advised it be turned off when driving in town. It will default to OD every time you restart the vehicle though, so I don't know how well anyone follows this recommendation.
On my Chevy the overdrive is always on. I carried a Genesis59 and 100gal fresh water tank with no problem. We don't have hills or mountains in Iowa though. If we did I'd turn it off more just because it changes your shift points in the lower gears. I'd do the same if I were towing alot of weight.
Fon Johnson
Member
- Joined
- Oct 15, 2006
- Messages
- 1,066
I never run in OD at all. I always leave it in 3rd. My Chevy has the 4L60 which was not the best tranny for the application. They did make some improvements in them. There is a 4L60HD available, and you can upgrade to the 4L80 (but it is a pain.) Most makers recommend turning OD off when towing, or in our case hauling a lot of weight.
My trans guy has been in the biz for over forty years. He told me if I don't use OD under 60 mph the trans will last twice as long. Manufacturers program the upshift too early to boost their c.a.f.e. (corporate average fuel economy) numbers.
First thing I do after starting the engine in my Ford is push the OD lockout button. I'll shift into OD on a long downhill.
First thing I do after starting the engine in my Ford is push the OD lockout button. I'll shift into OD on a long downhill.
Fon Johnson
Member
- Joined
- Oct 15, 2006
- Messages
- 1,066
If someone knew what they were doing, you could use a computer program to "re-flash" the computer. You can alter shift points, and even firm up the shifts. I've thought about buying one for myself to tune the hot rods..
OZ hit the nail on the head. Its the "hunting" between 3rd and 4th that kills the tranny. When I worked for a public works dept. we kept dropping transmissions in our chevy 3500s. for that reason. The mechanics locked out 4th in all the vehicles and we didn't lose any more.
Fon, I got a reprogrammed ECM from Westers tune for towing. Works great. More low end, and a little better mileage. The over the counter reprogrammers can only do so much. Check out http://westers_garage.eidnet.org/
Fon, I got a reprogrammed ECM from Westers tune for towing. Works great. More low end, and a little better mileage. The over the counter reprogrammers can only do so much. Check out http://westers_garage.eidnet.org/
Slipping and lack of coolant flow
The main trouble encountered with trannys is slipping of the clutches and a lack of coolant flow at lower engine rpms.
When a tranny has to pull hard against a load, the internal components and clutches 'slip' more than normal, building up heat from fluid friction. Even after the torque converter locks up in overdrive, slipping can occur greatly adding to heat build. Add to this that when the engine rpms are down, the fluid flow in the tranny is much slower, you can have a critical temp rise followed by rapid fluid degradation and eventual failure of the tranny. Gear 'hunting' is a bad signal of slippage.
By going into tow mode, the tranny usually stays in a lower gear, thus increasing fluid flow and allowing easier torque transfer. This translates to much lower fluid temps.
Personally, I decided to put gauges on to monitor the fluid temps and slippage %'s. If I notice excessive slippage, like towing heavy loads with my pickup, I'll drop it into tow mode. Or if the tranny temp climbs (stop and go traffic and backing up to trailers is terrible on temps), I'll kick it to a different gear to lower temps.
The main trouble encountered with trannys is slipping of the clutches and a lack of coolant flow at lower engine rpms.
When a tranny has to pull hard against a load, the internal components and clutches 'slip' more than normal, building up heat from fluid friction. Even after the torque converter locks up in overdrive, slipping can occur greatly adding to heat build. Add to this that when the engine rpms are down, the fluid flow in the tranny is much slower, you can have a critical temp rise followed by rapid fluid degradation and eventual failure of the tranny. Gear 'hunting' is a bad signal of slippage.
By going into tow mode, the tranny usually stays in a lower gear, thus increasing fluid flow and allowing easier torque transfer. This translates to much lower fluid temps.
Personally, I decided to put gauges on to monitor the fluid temps and slippage %'s. If I notice excessive slippage, like towing heavy loads with my pickup, I'll drop it into tow mode. Or if the tranny temp climbs (stop and go traffic and backing up to trailers is terrible on temps), I'll kick it to a different gear to lower temps.
